The present invention relates in general to telecommunications and, more particularly, to telecommunication systems for transmitting both audio and video signals from a local station to a remote station, as well as receiving audio and video from the remote station at the local station. Specifically, one embodiment of the invention provides a "videophone" apparatus and method which enable simultaneous audio and video telecommunication between stations connected by a standard bidirectional (full duplex) telephone line in the form of a twisted pair.
Telephones have been in widespread use for more than a century. As is well known, telephones enable a code comprising a telephone number to be entered at a local station. This code is employed to effectuate audio communication with a remote station identified by the code. The local and remote stations are connected through sophisticated telephone systems comprising wiring, automated switching networks responsive to entered codes, and, in the case of long distance, long-haul microwave links and/or oceanic wires or optical fiber cables for interconnecting the local and remote stations. The wiring that connects to the local and remote stations is typically a standard telephone line in the form of a twisted pair. These telephone systems are generally provided by regulated common carriers.
The configuration of current telephone systems does not per se constitute a part of the present invention and therefore will not be described in further detail, except to mention that the bandwidth of standard telephone systems is limited, as is well known. That is, the range of analog signal frequencies and the rate at which a digitally coded signal can be communicated by a standard telephone line are limited. As will become clear as the description continues, the major limiting factor and a problem addressed by one embodiment of the invention is that the effective (coded) synchronous digital bandwidth is believed to be less than approximately 56 kilobits per second (kbps). Stated differently, it would require the equivalent of 5,000 standard telephone lines to transmit television-quality pictures at the typical rate of 30 frames per second for television.
The concept of integrating video communication with the audio communication traditionally provided by the telephone is old. For example, at the 1964 World's Fair in New York City, American Telephone & Telegraph Company exhibited a "picture phone" by which both audio and video were bidirectionally communicated between local and remote stations. This picture phone added a television camera, television transmitter and receiver, and television monitor to the telephone assembly at each of the stations. Moreover, in order to transceive (that is, both transmit and receive) audio and video, a dedicated high-capacity telephone line having a bandwidth adequate for bidirectional communication between the local and remote stations was provided. In fact, a dedicated telephone line not generally available to the public, known as a T-3, was used. Hence, this picture phone was futuristic and considered cost prohibitive for widespread commercial deployment.
After a hiatus, audio and video communication between local and remote stations re-appeared in the form of "video teleconferencing." Video teleconferencing systems are typically based in dedicated local and remote rooms. These video teleconferencing rooms were initially equipped with a system similar to the 1964 World's Fair picture phone system. Generally, these video teleconferencing systems have evolved to comprise a video camera connected to a video processor which digitizes the video signal, in turn connected to a communication controller for transmitting video over a high-capacity data communications link (a high-capacity digital telephone line, such as a T-1) leased from a common carrier. The video portion of the video teleconferencing system also comprises one or more television monitors connected to the video processor for displaying video. Recently, data compression techniques have been employed to render video transmission more efficient. For optimum audio quality and apparent synchronization between audio and video, audio is provided over another leased telephone line. Audio can be communicated over a standard telephone line, but audio quality is compromised (e.g., cross-talk, etc.). Also, synchronization between audio and video suffers not only because audio and video are being transceived by two different subsystems, but also due to propagation delay. Propagation delay is evident in visible loss of synchronization between audio and video, such as lip movement not synchronized with speech, especially if long distances are involved, for example, America to Europe or Japan. In any event, audio and video are transceived over different telephone lines. Such video teleconferencing systems are commercially available from PictureTel Corporation of Peabody, Mass., and Compression Labs Inc. of San Jose, Calif., for example, but are priced at tens of thousands of dollars and are therefore affordable generally only by businesses, beyond the reach of the home consumer budget. Consequently, widespread deployment of these video teleconferencing systems has not occurred.
As an alternative to video teleconferencing, Matsushita Electric Ltd. introduced a still-image, black-and-white visual telephone (Model Number WG-R2) in 1987. This visual telephone integrated a small video camera, video digitizer, communication controller, and cathode ray tube (CRT) display into a housing connected to either the same standard telephone line as the telephone assembly at each of the local and remote stations or to a second standard telephone line if the stations were equipped with two-line service. In the case of a single telephone line, audio and video were transmitted alternately under manual control. That is, the persons at the stations discontinued speaking whenever it was desired to transmit video, one pressed a send button to transmit a video snapshot, and this video snapshot was transmitted to the remote station and displayed. Thereafter, the conversation could be resumed. Therefore, audio and video were not communicated simultaneously. In the case of two telephone lines, video operation was independent of audio, so that video snapshots could be transmitted from one station to another, while audio continued uninterrupted over the second telephone line. However, even in the case of two telephone lines, video snapshots could not be simultaneously exchanged between the local and remote stations, so the persons at the stations needed to coordinate video communication so that an access conflict did not arise. In any event, not only were audio and video non-simultaneous over the same telephone line, but only still video snapshots could be transceived, whereas video teleconferencing provides motion video. Also, if a second telephone line were desired, an on-going charge for two-line telephone service was incurred.
Therefore, it would be desirable to have a telecommunication system which would provide simultaneous audio and video communication over a single standard bidirectional (full duplex) telephone line. Moreover, it would be desirable that such a videophone provide audio synchronized with motion video.